Good-bye Shark Week? Large sharks in decline due to fishing

Large sharks are particularly vulnerable to fishing, a new review says. The …

Sharks have been honed into efficient predators by over 400 million years of evolution, but that didn’t prepare them for commercial-scale fishing. Sharks, skates, and rays are fantastically abundant in unexploited parts of the ocean, but a new review shows that even light fishing—both targeted at sharks and other species—can send populations into a tailspin. Large, top-predator shark species appear to suffer the most, and their dwindling numbers are drastically affecting many marine ecosystems.

The review, which appears in Ecology Letters, synthesizes dozens of research papers on sharks, skates, and rays to draw a picture of declining large shark populations. There has been a commensurate rise in what ecologists call mesopredators, like rays, small sharks, dolphins and turtles—animals one step down from apex predators.

Fishing operations appear to be at fault. Targeted commercial fishing, by-catch, and even subsistence fishing are rearranging the chips in many marine ecosystems, knocking large sharks from their positions as top predators and sending waves throughout the rest of the food web.

These conclusions may be somewhat surprising given that many sharks are renowned generalists, able to feast on a wide variety of prey. As a group, sharks also have been fantastically adaptable. They inhabit nearly all marine waters—coastal, open ocean, even the Arctic regions—and occupy a variety of niches. Despite their success, however, sharks are limited by their reproductive strategies. They mature sexually later and produce fewer offspring than bony fish, making them more like marine mammals in that sense. This sort of life history makes them particularly susceptible to overfishing.

More than 90 percent of all elasmobranch species—the collective name for sharks, rays, and skates—live close to the ocean floor on continental shelves and slopes. This makes them especially vulnerable to trawling. Surveys in the Gulf of Mexico between 1972 and 2002 revealed steep population declines of shallow water species—up to 99 percent in one case—that turn up as shrimp by-catch.

When trawling begins in an area, the researchers note that elasmobranch species diversity is often high, but it falls off as the practice continues. Large sharks tend to disappear, followed by a population boom of smaller sharks, rays, and skates.

Little is known about how shifting shark populations alter marine food webs, but the paper cites a few examples of sharks’ widespread influence. In South Africa, a decline in large shark numbers caused a boom in smaller inshore shark populations, which in turn sent bony fish stocks plummeting. In another case off the North Carolina coast, cownose rays are consuming more bay scallop than they have in the past. The rays aren’t hungrier—there were simply more of them because fewer large sharks are holding their numbers in check.

Large shark populations still exist in some more remote areas of the oceans, especially in the Pacific, but global shark catches continue to rise. The researchers think a change in fishing practices is also afoot, with many sharks now being actively fished instead of caught accidentally. Part of the cause, they state, is the popularity of shark fin soup in Asia. Still, they point out, by-catch from regular fishing remains the largest threat to the sleek marine predators.

I’d like to share a revelation that I’ve had, during my time here. It came to me when I tried to classify your species and I realized that you aren’t actually mammals. Every mammal on this planet instinctively develops a natural equilibrium with its surrounding environment, but you humans do not. You move to an area and you multiply, and multiply until every natural resource is consumed. The only way you can survive is to spread to another area. There is another organism on this planet that follows the same pattern. Do you know what it is? A virus. Human beings are a disease, a cancer of this planet. You are a plague, and we... are the cure.

Hmm, this larger observation goes against the local news up in MA the past few weeks. The news media has been reporting daily on the OMG SHARK! sightings around the Cape Cod area particularly. Something about warmer waters this summer has brought more sharks than usual to the area, even close to shore, causing beaches to close. It seems nearly every night the news is reporting another "POSSIBLE GREAT WHITE!!!" sighting. Sigh. Thanks to this, I'll have a hard time for a while convincing people up here that sharks worldwide are actually threatened. Personally, I'm not particularly surprised by the paper's conclusions. It seems to me that people have a harder time justifying protections for predators, as my casual observations don't see much efforts for the sharks. Or, are sharks just not cute enough? They're certainly plenty refined and cool enough.

You also have to consider that as an apex predator, large sharks play the important role of ensuring other species remain strong. Like lions on the savannah, they pick off the sick and weak from from other species, ensuring those populations are left with stronger, healthier stock for breeding. You remove that large, external pressure point, and populations can start intermingling weaker genetic combinations that wouldn't normally make it. Then a major catastrophe can strike, and that overall weakening of a species could mean more of them die in the catastrophe than would have normally if an apex predator had kept up the pressure to ensure only the strongest and healthiest survived to breed. There's just such a huge ripple effect.

The recent shark documentary that went through the movies had a lot more detail on declining shark populations and the practices that are leading this to occur. If you are interested in the subject, you should look it up.

I saw it at the cinemas, and it was really quite good - if disturbing.

My personal take on the subject is that sharks are a vital part of the ocean ecosystem, and we may be looking at terrible unforeseen consequences if current fishing practices are permitted to continue. At what point do you call bull$#!t when nations try to claim that animals that they have historically had no access to are part of their cultural diet? It's the same problem that occurs with whales, except that sharks don't enjoy the widescale good will of so many people worldwide.

No one should ever EVER eat shark fin soup. The sharks are de-finned and then thrown back into the water to drown! All for the fins which have no discernible taste anyway. They are in the same realms as rhino horns and tiger penises. i.e. a bunch of no dick fuck heads think they might get a hard on if they eat shark fin soup.

You have WAY more chance of dying in a car accident (or even been hit by lightning) than by being eaten by a shark. Shark attacks are very rare, but the media over hypes them, because it's "news"

What a bunch of clap trap. Great White populations have returned to seal areas because the food returned after they (they're food) were protected. As the populations of these supposed ecological food chain disasters start to explode, the sharks will return because dinner is served. Arrogant 'scientists' that think that human beings are a virus make me laugh. Sharks are a migratory species, and unlike stupid humans who live in a desert where nothing grows but cactus and rattlesnakes and scorpions, sharks move to where the FOOD IS! Did the census borough interview all the sharks? Or did they just go out and try to find them and they didn't see as many? You know...they call it FISHING for a reason...otherwise they would call it CATCHING!